How Do You Isolate the Position of a Radio Source?

Question: How do radio astronomers isolate radio emissions from space that are at frequencies of the commercial radio channels?  – Mathav

Answer:  In fact, we try not to make measurements at frequencies that correspond to those used be commercial services.  At other frequencies, though, we isolate the position of a radio emission source in the same way that an optical telescope would for a source of optical emission.  By pointing our radio telescope in the direction of an astronomical radio signal and isolating the exact position of the signal by moving the position of the radio telescope beam slightly to “peak-up” the signal on the sky we can accurately isolate its position.  This is essentially the same technique used with optical telescopes.

Jeff Mangum

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What Star Has the Largest Number of Known Planets?

Question: Someone asked “How many planets a stellar-planetary system can accommodate safely into a stable orbit around that star? What are the factors it depends on?” What I’m asking is what is the largest number of planets have been observed orbiting a star? I understand it’s in principal a nearly infinite number “could” orbit a star. What is the solar system with the most known planets? Thank you.  – Michael

Answer: Looking at the NASA Exoplanet Database, it appears to me that the current confirmed extrasolar planetary system with the most planets orbiting a single star is KOI-351 with seven planets.  Of course, our solar system is the champ with 8 planets and a host of dwarf planets if you want to count all stars with planets.

Jeff Mangum

 

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How Can Gas Particles Stick Together to Ultimately Form Stars and Planets?

Question: There is a lot of acceptance that when the gases of the universe began to join and spin because of the impact of those collisions. That would mean that all particles hit in the same direction, like using your hand to spin a basketball on your finger. When one questions this I just get blank stares as if I’m suggesting some sort of heresy. But, apart from the difficulty I have with the Big Bang being possible on it’s own (Quantum Physics suggests you need an outside force) the answers I read about the formation of planets and gravity seems absurd yet I can’t find anyone to explain it without theory and conjecture. Can someone help me. Just to make it clear what I’m asking, please help me understand how gas particles flying in every possible direction as can form into a rotating ball that turns into rock because physics itself suggests that is impossible. I use the theory that is used for the formation of planets as….

“…there was a massive cloud of hydrogen gas left over from the Big Bang. Some event, like a nearby supernova explosion triggered a gravitational collapse of the cloud, causing the hydrogen atoms to attach to one another through mutual gravity. Each individual hydrogen atom had its own momentum, and so when the atoms collected together into larger and larger clumps of gas, the conservation of momentum across all the particles set these clumps of gas spinning.”

Now that is a lot of conjecture – considering collisions from every possible direction…let alone how those hydrogen gas particles, once collected together formed everything we have on and in the planet.

– Brent

Answer: I think that the slight misunderstanding in your logic is the equate “sticking” with the gravitational attraction between particles such as atoms, molecules, and dust particles, which ultimately results in the formation of more massive objects like asteroids, comets, planets, and stars.  It is not necessary for objects to collide and “stick” to each other immediately.  A stable cloud of massive particles that is affected by a nearby event that “pushes” on it, such as a nearby supernova, will potentially be pushed in such a way that gravity causes objects to slowly move closer to each other and ultimately coalesce.  This slow collapse of massive objects toward other massive objects ultimately builds on itself, collecting larger and larger massive objects.  This ultimately is a mechanism for forming objects like planets, stars, and galaxies.

Jeff Mangum

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Can Time Dilation Near a Black Hole Explain the Orbits of Stars Near the Black Hole?

Question: Regarding galaxy rotation.  Although the supermassive black hole at the center of a Galaxy probably isn’t strong enough to speed up the rotation of its more distant stars so as to make the velocity curve level, nevertheless the time-dilation effect of such a black hole will make the orbital rotation speeds of the inner stars appear slower than it actually is as seen from the point of view of an observer outside the galaxy in question. Couldn’t this be a more reasonable explanation rather than hypothesizing ‘dark matter’?  – Tom

Answer: I don’t think that time dilation will affect the observed speed of stars near a black hole as observed from a point far from the black hole.  Time dilation affects what local observers measure, which means that the time measured by an observer at a star near a black hole will see time running slower than the time measured by the far-away observer.

Jeff Mangum

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Orientation of the NRAO 140 Foot Telescope Axis

Question: I was at the NRAO two days ago. Magnificent!  But in walking by the 140′ scope (by “Neptune”) it looked as though there was a mistake in the labeling on the informational sign.  On the diagram that explains how an equatorial mount works it purports to point to be pointing with a red arrow to the telescope axis parallel to the Earth’s axis. But the arrow is actually pointing to an earth radius at the base of the telescope (vertical axis to the center of the Earth). Was my understanding of the sign wrong or is the sign itself wrong. Sorry I could not take a digital photo of the sign in question to send (-;   By the way, I also found it unusual for scientists to be mixing their Imperial measurements up with the Metric, with a 140 foot telescope being located so close to a 30 meter one, for instance.  Wasn’t a space probe or space telescope destroyed by such confusion in its manufacture?  – Richard

Answer: I believe that your interpretation of the 140 foot telescope mount is correct, and that the diagram showing the arrow indicating the axis of the antenna pointing to an earth radius at the base of the telescope axis parallel to the Earth’s axis is not exactly correct.  It is the actual axis of the moving part of the antenna (the “polar axis”) that is parallel to the Earth’s axis.  Regarding the name of this telescope and its use of an Imperial unit, this is simply history and a desire not to rename.  We do work exclusively in a metric-based system, with few exceptions.  The one famous exception that you refer to, where a misunderstanding as to whether a calculation was done in metric or imperial units in a critical piece of software, caused the Mars Climate Orbiter to dip too deeply into the atmosphere of Mars and burn-up in 1999.

Jeff Mangum

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What Would a Neutron Star Look Like to the Human Eye When Viewed from 10 Light Years Away?

Question: What would a neutron star look like to the human eye from, say, 10 light years?  – Lee

Answer: Neutron stars emit most of their thermal radiation at x-ray wavelengths, and emit very little radiation (i.e. “light”) at optical wavelengths.  Therefore, at optical wavelengths, a neutron star even just 10 light years away would be very faint, and would be too faint to be seen with the unaided eye.

Jeff Mangum

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Is There a Period When the Radio Transmission Environment in the NRQZ is “Quieter”?

Question: I know the NRAO is located in a “radio quiet zone.”  Is there a time during the 24 hour day that is “quietest” for you there?  A time you would choose to listen for your weakest signals?   If there is, can you tell me that time?  – Robert

Answer: I am not aware of any times of the day when the general radio transmission environment is “quieter” than it is at other times.  There are radio transmitters that are time and position variable (such as radar devices attached to cars).  For information, the National Radio Quiet Zone (NRQZ) web page has some additional information about this area.

Jeff Mangum

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Questions About a Career in Astronomy

Question: Though I have taken physics chemistry and biology but not maths in my high school but recently i have Developed quite an interest in astronomy and I want to pursue my career in this field so is there any hope for me to do so? .And also please tell what should I do to do so?  – Zainab

Answer: You should look over the posts on my Careers in Astronomy section.  There you will find lots of responses to questions about how one can pursue a career in astronomy.

Jeff Mangum

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What Are Those Two Bright Lights on the Western Horizon?

Question: On July 15, 2015, observing from Las Vegas, Nevada, there are 2 objects (Low) in the Western sky. One is bright the other dim. Are they Venus and Jupiter?  – George

Answer: Yes!  Venus, the brighter of the two, is to the south (left when facing west) of the other bright guy, Jupiter.

Jeff Mangum

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What is that Bright Object in the Western Sky After Sunset?

Question: What bright light is in nepa’s sw sky at 30degrees above the horizion at 9:15 edt.  – Tom

Answer: Although I don’t exactly know what location you are observing from, I suspect that you are seeing Jupiter and Venus, which are both currently visible on the western horizon after sunset.

Jeff Mangum

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